There is an increasing use of cellular therapy in which modified, or unmodified cells are administered to a patient. An example of a cellular therapy is adoptive T cell transfer after CD34+ stem cell transplantation. Administering T cells after stem cell transfer helps to accelerate the reconstitution of an immune system in the patient recipient. When a matched related or unrelated donor is not available, or the disease is too aggressive for an extensive donor search, the use of an HLA haploidentical family donor may be effective. Such donors may be parents, siblings, or second-degree relatives. Such infusions may enhance immune recovery and thereby reduce virus infections and eliminate relapsing leukemia cells. However, the coexistence of alloreactive T cells in a donor stem cell graft may cause graft-versus-host disease (GvHD) in which the donor cells react against the recipient, which may progressively damage the skin, gut, liver, and other organs of the recipient, often with fatal consequences.
Other examples of cell therapies include using native cells or cells genetically engineered to express a heterologous gene. These treatments are used, for example, for blood disorders, but these therapies may have negative side effects. In other methods, immature progenitor cells that can differentiate into many types of mature cells, such as, for example, mesenchymal stromal cells, may be used to treat disorders by replacing the function of diseased cells.
Methods for inducing selective apoptosis using a Caspase-9 system, using ligand-mediated dimerization and activation of a chimeric Caspase-9 polypeptide are discussed in U.S. patent application Ser. No. 13/112,739, filed May 20, 2011, and entitled METHODS FOR INDUCING SELECTIVE APOPTOSIS, naming Malcolm K. Brenner as inventor, which is hereby incorporated by reference herein in its entirety.
There is a need for a rapid and effective mechanism to remove possible negative effects of donor cells used in cellular therapy, by providing an inducible Caspase system with lower basal activity.